<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>天气案例-简写</title>
    <script src="../js/vue.js"></script>
</head>
<body>
    <div id="root">
        <h2>今天天气很{{info}}</h2>
        <button @click="changeWeather">切换天气</button>
    </div>
</body>

<script>
    const vm=new Vue({
        el:'#root',
        data:{
          isHot:true,
        },
        computed:{
            info(){
                return this.isHot?'炎热':'凉爽'
            }
        },
        methods:{
            changeWeather(){
                this.isHot=!this.isHot
            } 
        },
        //也可以监视info
        watch:{
            isHot:{
                //不需要immediate和deep的时候

                //immediate:true,//初始化时让handler调用一下
                //deep:true,
                //handler调用：当isHot发生改变的时候
                /*handler(newValue,oldValue){
                    console.log(newValue,oldValue)
                }*/


                //目标名称可以当函数名
                /*isHot(newValue,oldValue){
                    console.log(newValue,oldValue)
                }*/
            }
           
        }
    })
    /*vm.$watch('isHot',{
        immediate:true,
        deep:true,
        handler(newValue,oldValue){
            console.log(newValue,oldValue)
        }
    })*/
    //不能配置immediate和deep
    //不能写箭头函数
    vm.$watch('isHot',function(oldValue,newValue){
        console.log(newValue,oldValue)
    })
</script>

</html>